1. Field of the Invention
This invention relates to active optical systems and more particularly to an active optical system for changing the wavelength of an incoming optical image.
2. Description of the Related Art
Frequently, in opto-electronic applications, devices exist that require inputs within a certain wavelength band. Unfortunately, due to optical hardware constraints such as laser output wavelength, optimum optical fiber transmission wavelength, etc., there are frequently mismatches between an image""s actual wavelength and the wavelength required for operation in a certain optical device. Typically, converting an image (or two-dimensional signal array) from one wavelength to another requires changing the optical signal to an equivalent electronic signal and reconverting the electronic signal to a wavelength within the desired band. This causes signal processing bottlenecks, reduced speed, reduced bandwidth as well as increased size, weight, volume and complexity of the associated optical hardware.
U.S. Pat. No. 6,046,841, issued to Mahgerefth et al., discloses and all-optical wavelength conversion system having an optical discriminator. The optical signal produced by a semiconductor-optical-amplifier based wavelength converter is passed through an optical discriminator. The resulting signal has improved extinction ratio for return-to-zero data and improved high-frequency response for both non-return-to-zero and return-to-zero data.
U.S. Pat. No. 6,137,624, issued to Taira, discloses a wavelength converting device comprising a plurality of nonlinear optical crystals for transmitting light by second harmonic generation. Each crystal piece has a crystal axis respectively and is positioned with the crystal angle satisfying a phase matching condition for second harmonic generation and so that the adjacent crystal axis is oriented in a crystallographically different way. In one embodiment, the acceptance angle, xcfx86, in the insensitive direction becomes the same as the acceptance angle, xcex8, in the sensitive direction. Therefore, there is no need for gathering light to an oval shape, and maximum conversion efficiency can be obtained by gathering light with a conventional spherical lens.
U.S. Pat. No. 6,211,999, issued to Gopalan et al., discloses a lithium tantalate single-crystal and photo-functional device. Provided are a lithium tantalate single-crystal that requires a low voltage of not larger than 10 kV/mm for its ferroelectric polarization inversion and of which the polarization can be periodically inverted with accuracy even at such a low voltage, and a photo-functional device comprising the crystal. The crystal has a molar fraction of Li.sub.2 O/(Ta.sub.2 O.sub.5+Li.sub.2 O) of falling between 0.492 and 0.50. The functional device can convert a laser ray being incident thereon or can be used as a physical memory.
U.S. Pat. No. 6,215,580, issued to Kouta, discloses a wavelength converter for generating optical harmonics of incident laser light at high efficiency and a method for varying wavelength of incident laser light. Nonlinear optical crystal xcex2BaB2O44 is available for generating optical harmonics of incident laser light, and an absorption spectrum shifter, a heat sink and a walk-off angle compensator are selectively provided for the non-linear optical crystal for increasing the efficiency of generating the optical harmonics.
The present invention is an active optical system for changing the wavelength of an incoming optical image. It includes a first control optics assembly for receiving an incoming optical image and adjusting that incoming optical image in accordance with first desired wavelength and beam propagation parameters. A template optical element produces a template optical intensity profile. A second control optics assembly receives the template optical intensity profile and adjusts that template optical intensity profile in accordance with second desired wavelength and beam propagation parameters. A polarization separator receives an output from the second control optics and polarizes the second control optics output. A quarter wave plate receives the polarized output from the polarization separator and changes its linear polarization into a circular polarization. A combiner receives an output from the first control optics assembly and an output from the quarter wave plate. The combiner provides a combined, co-linear propagation output image having an initial beam size. A spatial light modulator (SLM) addressing optics receives the combined, co-linear propagation output image and produces a desired beam size for the combined, co-linear propagation output image. An SLM receives the output from the SLM addressing optics and provides absorption of a portion of the combined, co-linear propagation output image. The absorbed portion is the incoming optical image. This absorption changes the local index of refraction of the SLM so that the local reflection at the template optical intensity profile changes. The template optical intensity profile reproduces the image of the absorbed portion as an outgoing image. The outgoing image is reflected back through the quarter wave plate via the combiner and rotated 90xc2x0relative to the template optical intensity profile by the quarter wave plate. It is separated by the polarization separator, thus providing a converted image having substantially the same intensity pattern as the incoming optical image but a different wavelength.
The present system produces copies of the input signal image intensity at a different wavelength. The device works in a manner that allows direct optical to optical translation, without having to change the signal into an electronic incarnation. This invention allows converting the wavelength to one within the desired band while the signal remains in an optical state. With a direct optical to optical translation, bottlenecks do not form and the bandwidth of the overall system is not affected by the wavelength changing hardware.